The RDF Schema document says
RDF's vocabulary description language, RDF Schema, is an extension
of RDF. It provides mechanisms for describing groups of related
resources and the relationships between these resources. RDF Schema
vocabulary descriptions are written in RDF. The extra descriptive
power of RDF Schema is carried in a collection of RDF resources
described in this document.
However, this is very unclear as to just what RDF Schema is. Is RDF Schema
just a collection of RDF resources, like the representation of DC in RDFS?
This is, of course, incorrect, as RDF Schema is a semantic extension of
RDF, as detailed in RDF Semantics. However, this is nowhere indicated in
the RDF Schema document.